run spec2k benchmarks as part of regular testing

_From [derek.br...@gmail.com](https://code.google.com/u/117968039472581148324/) on December 10, 2010 17:58:11_

PR 501222

We should add spec2k tests to some nightly test suite: it would have caught PR 494169 much much earlier, and would have confirmed the vfork bug that I caught via a post-code-review code review but was ignored for months afterward (PR 403015)

We should also run spec2k ref on a weekly basis to catch perf regressions

_Original issue: http://code.google.com/p/drmemory/issues/detail?id=168_